Path for properties file and license

How to define relative path to properties file in the desktop application? I want to demand user to create properties file and point path to license in his application (application will be using my component).
For example user can create application, put my jar in lib directory and put license somewhere else inside of his application. After that he has to create lic.properties file and point the path to license file there. But I don't want to ask him supply full path to lic.properties file and license file as full path of OS.
I would like to work with relative path. But relative to what? what is the root of desktop application and how it can be found?